Hollow plastic microspheres can be used in all standard processing methods for thermoset and thermoplastic composites. Microspheres are produced for a variety of applications using a fairly broad range of materials. Although they have less compressive strength than glass microspheres, hollow plastic microspheres offer many of the same advantages as rigid glass microspheres and are among the lightest fillers available. Standard specific gravities are as low as 0.015, providing large volume displacement at a very low weight.
Regulations promulgated under the federal Occupational Safety and Heath Act make reference to particulates not otherwise regulated (“PNOR”). Such PNOR materials include “all inert or nuisance dusts, whether mineral, inorganic, or organic” that do not have an assigned PEL, contain <1% quartz and do not contain asbestos. See, 29 CFR 1910.1000 TABLE Z-1 at footnote (f). Under these federal regulations, the Permissible Exposure Limits as 8-hour Time Weighted Averages are 15 mg/m3 for all PNORs, and 5 mg/m3 for respirable PNORs. Respirable sized particles are defined by OSHA as less than 3.5 microns in size.
Hollow plastic microspheres utilized as fillers in resin system are generally between about 12 to about 300 microns in diameter. This being the case, airborne hollow plastic microspheres are generally regulated as PNORs.